The present invention relates to a pipe bending machine.
In the bending of pipes, it is generally endeavoured to form successive bends to have the same radius of curvature so that the bending template does not have to be changed during the bending process. However, there are many occasions in which a uniform bending radius is not appropriate or possible. Thus, for example, in the bending of exhaust pipes for motor vehicles it is desirable to calculate the radius of curvature in order to provide a certain back-pressure in the exhaust pipe. This calculated radius is not necessarily appropriate for all of the bends in the pipe however.
In German (Federal Republic) published specification (Offenlegungsschrift) No. 21 01 162 there is disclosed a fully automatic method of bending pipes on a numerically controlled pipe bending machine to provide several different bending radii but without change or alteration of the clamped position of the pipe during its advance. To this end, several bending templates of different diameter are coaxially arranged on a bending table one above the other, thus in the form of storeys. During the changeover from one bending template to another, a clamping sleeve carrying the pipe on an advancing carriage is appropriately raised or lowered. As a result, the formation of bends of different radii takes place in different planes. The raising and lowering of the clamping sleeve carrying the pipe cannot be performed rapidly, because the weight is substantial. In addition, the entire system generally involves a complicated construction.
Bending templates layered in the manner of storeys are also disclosed in U.S. Pat. Nos. 3,299,681 and 3,147,792. During changeover from one bending template to another, the desired new template is driven by a spindle into the appropriate setting. Although the bending of the pipes always takes place in the same plane in this case, the raising and lowering of the bending templates through a single spindle is time-consuming. Moreover, the bending machines are bulky in the region of the templates.
In German (Federal Republic) Patent Specification No. 27 46 721 there is disclosed a pipe bending machine in which templates are arranged to be axially displaceable relative to each other, wherein in an initial setting an outer annular template surrounds an inner template. In this arrangement, it is necessary, during bending with bending templates of different radii, to laterally displace the advancing carriage with the clamping sleeve carrying the pipe to be bent. This operation requires a corresponding amount of time.